Floating Disks: An Investigation of Photosynthesis
Teacher Materials
Learning Goals, Objectives, and Skills................................................................ 2
Standards Alignments........................................................................................... 3
Laboratory Set-Up Manual .................................................................................... 5
Instructor Laboratory Guide ................................................................................. 6
Answers to Student Questions ............................................................................ 7
Post-Lab Extension Activities .............................................................................. 9
*Please consider adapting this lab to include some student-centered investigation.
Some suggestions, ideas, and tips can be found in a separate document called
"Student-Centered Investigation”
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Floating Disks: An Investigation of Photosynthesis
Learning Goals, Objectives, and Skills
Student Learning Goals:
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Students will understand the basic process of photosynthesis.
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Students will understand the role of environmental factors in photosynthetic rate.
Student Learning Objectives:
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Students will articulate the function of photosynthesis and identify the reactants and products of
this reaction.
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Students will measure the effect of light and other factors on photosynthesis.
Scientific Inquiry Skills:
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Students will pose questions and form hypotheses.
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Students will design and conduct scientific investigations.
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Students will make measurements and record data.
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Students will use mathematical operations to analyze and interpret data.
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Students will generate tables and graphs to present their data.
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Students will use experimental data to make conclusions about the initial question and to support
or refute the stated hypothesis.
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Students will follow laboratory safety rules and regulations.
Laboratory Technical Skills:
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Students will demonstrate proper use of micropipettors.
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Floating Disks: An Investigation of Photosynthesis
Standards Alignments
MA Science and Technology/Engineering Curriculum Framework (2006)
Biology
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1.2 Describe the basic molecular structures and primary functions of the four major categories of
organic molecules (carbohydrates, lipids, proteins, nucleic acids).
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2.4 Identify the reactants, products, and basic purposes of photosynthesis and cellular respiration.
Explain the interrelated nature of photosynthesis and cellular respiration in the cells of photosynthetic
organisms.
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2.5 Explain the important role that ATP serves in metabolism.
Chemistry
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7.5 Identify the factors that affect the rate of a chemical reaction (temperature, mixing, concentration,
particle size, surface area, catalyst).
Scientific Inquiry Skills
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SIS1. Make observations, raise questions, and formulate hypotheses.
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SIS2. Design and conduct scientific investigations.
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SIS3. Analyze and interpret results of scientific investigations.
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SIS4. Communicate and apply the results of scientific investigations.
Mathematical Skills
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Construct and use tables and graphs to interpret data sets.
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Solve simple algebraic expressions.
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Perform basic statistical procedures to analyze the center and spread of data.
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Measure with accuracy and precision (e.g., length, volume, mass, temperature, time)
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Use common prefixes such as milli-, centi-, and kilo-.
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DRAFT REVISED MA Science and Technology/Engineering Standards (2013)
*Please note that these are DRAFT standards that have not yet been submitted for formal review or
adoption.
Biology
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HS-LS1-5. Use a model to illustrate how photosynthesis uses light energy to transform carbon
dioxide and water into oxygen and chemical energy stored in the bonds of glucose and other
carbohydrates.
[Clarification Statement: Emphasis is on illustrating inputs and outputs of matter (including ATP) and the transfer and
transformation of energy in photosynthesis by plants and other photosynthesizing organisms. Examples of models could
include diagrams, chemical equations, and conceptual models.]
[Assessment Boundary: Assessment does not include specific biochemical steps of light reactions or the Calvin Cycle, or
chemical structures of molecules.]
•
HS-LS2-3. Construct and revise an explanation based on evidence that the processes of
photosynthesis, chemosynthesis, and aerobic and anaerobic respiration are responsible for the
cycling of matter and flow of energy through ecosystems. Explain that environmental conditions
restrict which reactions can occur. [Clarification Statement: Examples of environmental conditions can include the availability of sunlight or oxygen.]
[Assessment Boundary: Assessment does not include the specific chemical processes of photosynthesis, chemosynthesis, of
either aerobic respiration or anaerobic respiration.]
Chemistry
• HS-PS1-5. Construct an explanation based on collision theory for why varying conditions influence
the rate of a chemical reaction or a dissolving process. Design and test ways to alter various
conditions to influence (slow down or accelerate) rates of processes (chemical reactions or
dissolving) as they occur.
[Clarification Statement: Explanations should be based on three variables in collision theory: quantity of collisions per unit time,
molecular orientation on collision, and energy input needed to induce atomic rearrangements. Conditions that affect these
three variables include temperature, pressure, concentrations of reactants, mixing, particle size, surface area, and addition of a
catalyst.]
[Assessment Boundary: Assessment is limited to simple reactions in which there are only two reactants and to specifying the
change in only one variable at a time.]
NRC Practices
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Asking questions and defining problems
Planning and carrying out investigations
Analyzing data
Mathematical and computational thinking
Constructing explanations and designing solutions
Engaging in argument from evidence
Obtaining, evaluating, and communicating information
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Floating Disks: An Investigation of Photosynthesis
Laboratory Set-Up Manual
Note: The set-up procedure below is designed for groups of two.
Supply List:
For lab preparation:
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•
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5 × light sources, such as 15 watt spiral fluorescent bulbs
2 g baking soda
liquid dish detergent
For each group:
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2–3 × fresh young spinach leaves or about 8 plant seedlings
2 × 5-cm lengths of drinking straws (4–5 straws should be plenty)
3 × 10-mL syringes (20 if just testing light vs. dark with no control)
1 × small containers such as cups or 100-mL beakers
2 × 250-mL beakers
1 × aluminum foil squares, approximately 10 cm × 10 cm
Tips for supplies:
Fresh baby spinach leaves can be purchased from any grocery store. A 1-lb bag should be sufficient. As
an alternative, students could grow young plants using radish seeds or Wisconsin Fast Plant seeds.
Seeds should be planted 5–7 days before the day of the experiment.
Lab Set-up Calendar
2 weeks before lab:
¨ Check supplies and order any needed materials.
¨ If making any substitutions to the supply list, edit the student protocol accordingly.
1 week before lab: (Optional)
¨ Plant radish or Wisconsin Fast Plant seeds.
2–3 days before lab:
¨ Purchase fresh baby spinach leaves..
1 day before lab:
¨ Set up student lab stations with all durable materials.
¨ Set up lights.
Morning of lab:
¨ Add 2 grams baking soda to 500 mL tap water. Stir or shake until dissolved.
¨ Add 3 drops detergent to the baking soda solution, gently stir, try not to create too many bubbles
¨ Aliquot 35 mL of baking soda/detergent solution into each of 15 100-mL beakers or small cups and
distribute to lab stations.
Beginning of class:
¨ Distribute 2–3 leaves OR 8 seedlings to each lab station.
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Floating Disks: An Investigation of Photosynthesis
Instructor Laboratory Guide
Laboratory Procedure Tips:
1. Before starting the experiment, ask students to check their materials list to make sure they have
everything.
2. Students will be working in groups of two, make sure both students actively participate in the lab.
3. Be sure to demonstrate the procedure for creating the vacuum in the syringe. It is important that
students make a tight seal with their thumb while pulling back with the other hand. The vacuum
should be “held” for five seconds and then released.
4. When expelling the air from the syringe or releasing the vacuum, the students should be careful
to avoid pointing the tip of the syringe at their peers—sometimes the solution can squirt out.
5. Students may have to repeat the vacuum procedure several times to get all the disks to sink.
However, it is possible to “overdo it,” and damage the leaf tissue. If students have tried several
times and the leaf disks are not sinking, suggest they get fresh disks.
6. If you are in an interior, windowless room, make sure that all the overhead lights are on to
maximize the ambient light. Please note: Depending on the ambient light, the control disks may
not float—this is not unusual.
7. During the wait time, you could suggest one of the following to keep your students engaged:
• Ask students to design a modified experiment to test other variables.
• Choose from the suggested post-lab extension activities.
• Give them a diagram of a non-plant eukaryotic cell and ask them to modify the diagram to
make it a plant cell. Have them indicate where the processes of photosynthesis and
cellular respiration occur.
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Floating Disks: An Investigation of Photosynthesis
Answers to Student Questions
Protocol-Embedded:
p. 2:
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Sample answer: You could measure the rate of photosynthesis by collecting released O2 or by
figuring out how much glucose the plant has produced. You could also measure how much CO2
is used up.
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The lead disks float initially because there are air spaces between the cells. The trapped air,
makes the leaf disks less dense than water.
Pre-Lab:
1. The baking soda (NaHCO3) is the source of carbon which the cells use to make glucose.
2. Experimental controls help to show that any results you get are caused by the variable you’re
testing.
3. The syringe in ambient light serves as the control.
4. No we expect the disks in each tube will behave differently. The leaf disks will photosynthesize
more or less depending upon the light conditions. Under the bright light the disks can
photosynthesize more and as a result produce more glucose and O2. The disks in ambient light
may have enough light to photosynthesize and if so they will also float, but it will take longer to
produce enough O2 for each disk to float., The disks in the dark will not float because
photosynthesis requires energy from light.
5. Photosynthesis releases oxygen, which displaces the detergent solution in the intercellular
spaces and makes the leaves less dense than water.
Post-Lab and Analysis:
1. Expected answer: The tube under the bright light had the most floating disks. This matches my
pre-lab prediction.
2. The higher the light intensity, the more energy available for the reactions of photosynthesis, so
the faster the rate of photosynthesis. More photosynthesis produces more glucose and O2. The
air is trapped between the cells and makes the leaf disks less dense than water. Our data shows
that the disks under bright light floated faster than those under ambient light, and the disks in the
dark did not float at all.
3. Sample answer: I’d expect that none of the disks would float in any of the tubes. Photosynthesis
requires enzymes, and enzymes will denature if they are boiled.
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Sample data table:
Time (minutes)
Number of Leaf Disks Floating
Bright light
Ambient light
No light
0
0
0
0
5
0
0
0
10
1
0
0
15
5
0
0
20
6
0
0
25
7
1
0
30
8
1
0
35
9
2
0
40
10
1
0
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Floating Disks: An Investigation of Photosynthesis
Post-Lab Extension Activities
Student Oral Presentation:
Students can report the findings of their student-centered investigations to the class using a PowerPoint
presentation that includes the following information:
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Experimental question—what you hope to learn from performing the experiment.
Hypothesis—a testable, proposed answer to the experimental question based on prior
knowledge.
Experimental system and data collection methods—flowchart of how the experiment was
performed and how data was collected. This should NOT include a detailed summary.
Results—observations, data tables, figures, etc.
Conclusions—should the hypothesis be accepted or rejected as supported by key data.
Online resource for effective PowerPoint presentations:
http://office.microsoft.com/en-us/powerpoint-help/tips-for-creating-and-delivering-an-effectivepresentation-HA010207864.aspx
Student Lab Report:
Students can report the findings of their student-centered investigations through a written lab report. Your
school may have its own lab report format, but generally lab reports include the following information:
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Title—brief summary reflecting the factual content of the investigation.
Introduction—includes questions being answered, hypothesis and background information.
Materials—list of supplies needed to perform the lab.
Procedure—step-by-step procedure (with enough detail so someone could repeat the
experiment).
Results—observations, data tables, figures, etc. and a brief narrative summary of results.
Conclusion—explanation supported by evidence for whether the hypothesis should be accepted
or rejected.
Online resources for writing lab reports:
http://www.mhhe.com/biosci/genbio/maderinquiry/writing.html
http://www.ncsu.edu/labwrite/
Student Writing Exercise:
Ask students to read a current newspaper or journal article related to biofuels and write a paragraph
answering a series of prompts. For example, students could read the online article, How plants can suck
water from the sky (http://www.saps.org.uk/secondary/news-and-research/1267-how-plants-can-suckwater-from-the-sky ) and write a response to the following statement: “The discovery that some plants can
collect water from the atmosphere will revolutionize agriculture.”
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How plants can suck water from the sky
How does water travel through a plant? Your answer's probably a simple one. Water moves from the soil,
up through the roots and stems of a plant, through the leaves and out into the surrounding atmosphere.
But recent research has shown that our traditional understanding of the movement of water through
plants is incomplete. Under certain specialised conditions, some plants have evolved the ability to absorb
water through their leaves, move it down the xylem, and them release it into the soil. The plants are
actually watering their own roots - and their own seedlings. This off-beat mechanism for water uptake
works well enough that these plants can continue to photosynthesise and grow, even when the soil they
are growing in are dry.
The trees the researchers studied - Drimys brasiliensis - grow in the cloud forests of Brazil, where the
trees are almost constantly covered in fog. The atmosphere around the leaves has a higher water
potential than the leaves themselves, allowing foliar water uptake. The exact pathway for water entry is
still under discussion: this particular species has a hydrophilic cuticle that could facilitate water entry, as
well as hydrophilic tissues within the leaf that could provide water storage.
At least 70 species, across seven different ecosystems, have been identified as using this 'back-to-front'
water transport mechanism, pulling water out of the sky and down to the rhizosphere.
These new findings have important implications for our existing models of the climate and our
ecosystems, which often consider soil water as the only source of water for plants.
It's another example of how plants are constantly over-turning our expectations.
Source: Science & Plants for Schools, Biology News. Accessed 12 August 2014.
Eller, C. B., Lima, A. L. and Oliveira, R. S. (2013), Foliar uptake of fog water and transport belowground
alleviates drought effects in the cloud forest tree species, Drimys brasiliensis (Winteraceae). New
Phytologist, 199: 151–162. doi: 10.1111/nph.12248
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Websites:
http://mudshark.brookes.ac.uk/CAPP
http://www.natureworldnews.com/articles/7991/20140710/researchers-capture-images-photosynthesisaction.htm
http://www.igb.illinois.edu/news/illinois-improve-crop-yield-through-photosynthesis-new-global-effort
Videos:
https://www.youtube.com/watch?v=g78utcLQrJ4
Games:
http://earthguide.ucsd.edu/earthguide/diagrams/photosynthesis/photosynthesis_game.html
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&ved=0CEEQFjAD&url=http%3A%
2F%2Foutreach.mcb.harvard.edu%2Fteachers%2FSummer09%2FEdBarry%2FPhotosynthesisGame.ppt
&ei=9jHqU8awFI78yQTd8oCoBg&usg=AFQjCNFjHLxEFw8x9yvvLWMHcraj9cwMfQ&sig2=3ito6gdlpDi1y
ZWAcZaDQA
http://www.ellenjmchenry.com/homeschool-freedownloads/lifesciencesgames/photosynthesisformula.php
Related Experiments:
http://www.biologyjunction.com/5b-photoinleafdiskslesson.pdf
http://www.phschool.com/science/biology_place/labbench/lab4/intro.html
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Practice MCAS Questions:
The following multiple-choice questions from the spring 2013 and spring 2010 Biology MCAS test probe
student understanding of the interconnectedness of photosynthesis and cellular respiration.
Which of the following statements describes a difference between photosynthesis and cellular respiration in plants? A. Photosynthesis occurs only during the day, whereas cellular respiration occurs only at night. B. Photosynthesis involves only one reaction, whereas cellular respiration involves many steps. C.
Photosynthesis occurs only in cells containing chlorophyll, but cellular respiration occurs in all cells. D. Photosynthesis converts light energy into chemical energy, but cellular respiration converts light energy into heat energy. Which of the following statements correctly describes the processes of photosynthesis and cellular respiration? A. Photosynthesis and cellular respiration occur in the same organelle. B.
Photosynthesis and cellular respiration are performed by all organisms. C.
Photosynthesis produces carbon dioxide, and cellular respiration uses carbon dioxide. D. Photosynthesis stores energy for cells, and cellular respiration releases energy for cells. The following open-response question from the spring 2012 Chemistry MCAS test probes student
understanding of photosynthesis.
Sample student responses can be found at:
http://www.doe.mass.edu/mcas/search/answer.aspx?questionid=23790
• BE SURE TO ANSWER AND LABEL ALL PARTS OF THE QUESTION. • Show all your work (diagrams, tables, or computations) in your Student Answer Booklet. • If you do the work in your head, explain in writing how you did the work. Glucose (C6H12O6) is formed in plants by the process of photosynthesis. The net equation for photosynthesis is shown below. sunlight 6CO2 + 6H20 -­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐→ C6H12O6 + 6O2 a. Calculate the molar mass of glucose. Show your calculations and include units in your answer. b. Explain how the amount of carbon dioxide consumed by a plant can be determined from measuring the amount of oxygen released by the plant. Assume excess water is available. c. Calculate the amount of glucose, in grams, formed when 100 mol of O2 is released. Show your calculations and include units in your answer. 12
Practice AP Exam Questions: The following multiple-choice questions was pulled from the fall 2012 AP Biology Course and Exam
Description booklet.
A student placed 20 tobacco seeds of the same species on moist paper towels in each of two petri dishes. Dish A was wrapped completely in an opaque cover to exclude all light. Dish B was not wrapped. The dishes were placed equidistant from a light source set to a cycle of 14 hours of light and 10 hours of dark. All other conditions were the same for both dishes. The dishes were examined after 7 days, and the opaque cover was permanently removed from dish A. Both dishes were returned to the light and examined again at 14 days. The following data were obtained. Dish A Dish B Day 7 Covered Day 14 Uncovered Day 7 Uncovered Day 14 Uncovered Germinated seeds 12 20 20 20 Green-­‐leaved seedlings 0 14 15 15 Yellow-­‐leaved seedlings 12 6 5 5 8 mm 9 mm 3 mm 3 mm Mean stem length below first set of leaves According to the results of this experiment, germination of tobacco seeds during the first week is (A)
(B)
(C)
(D)
increased by exposure to light unaffected by light intensity prevented by paper towels accelerated in green-­‐leaved seedlings Additional observations were made on day 21, and no yellow-­‐leaved seedlings were found alive in either dish. This is most likely because (A)
(B)
(C)
(D)
yellow-­‐leaved seedlings were unable to absorb water from the paper towels taller green-­‐leaved seedlings blocked the light and prevented photosynthesis yellow-­‐leaved seedlings were unable to convert light energy to chemical energy a higher rate of respiration in yellow-­‐leaved seedlings depleted their stored nutrients 13